1. Field of the Invention
This invention relates to a hinge ball for a variable capacity wobble plate compressor and a hardening coil therefor, and more particularly to a hinge ball for a variable capacity wobble plate compressor and a hardening coil therefor, which are capable of reducing wear of sliding portions of component parts to thereby prevent offensive noise from being produce during use thereof.
2. Description of the Prior Art
A conventional variable capacity wobble plate compressor has been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 3-986, which is shown in FIG. 7. As shown in the figure, a shaft 505 has a thrust flange 540 rigidly fitted thereon, and a drive hub 541 rotatively mounted thereon via the hinge ball 509. The thrust flange 540 and the drive hub 541 are linked to each other by a link arm 542, whereby the rotation of the shaft 505 is transmitted from the thrust flange 540 to the drive hub 541. A wobble plate 510 is mounted on a boss 543 of the drive hub 541. The wobble plate 510 is linked via a connecting rod 511 to a piston 507. With rotation of the shaft 505, the trust flange 540 and the drive hub 541 rotate in unison with the shaft 505, and as the drive hub 541 rotates, the wobble plate 510 performs wobbling motion about the hinge ball 509. The wobbling motion of the wobble plate 510 is transmitted via the connecting rod 511 to the piston 507, to thereby transform the wobbling motion into a linear reciprocating motion of the piston 507.
As shown in FIG. 8, the hinge ball 509 has a central through hole 527 through which the shaft 505 loosely extends. An inner peripheral surface 509a of the hinge ball 509 is in sliding contact with an outer peripheral surface of the shaft 505, and the hinge ball 509 can be moved along the axis of the shaft 505. Further, an outer peripheral surface 509b of the hinge ball 509 is in sliding contact with an inner peripheral surface of a boss 543 of the drive hub 541.
The outer peripheral surface 509b of the hinge ball 509 is formed in a convex shape, and the inner peripheral surface of the boss 543 is formed in a concave shape, with the outer peripheral surface 509b of the hinge ball 509 being fitted in the inner peripheral surface of the boss 543 of the drive hub 541. The inner peripheral surface of the boss 543 of the drive hub is in sliding contact with the outer peripheral surface 509b of the hinge ball 509, and the drive hub 541 can be slid on the outer peripheral surface 509b of the hinge ball 509.
However, the shaft 505 is made of SMNC21 which has a high hardness. In contrast, the drive hub 541 is made of FCD600 (ductile cast iron) with a low hardness in consideration of the shaping requirements thereof. Therefore, there is a large difference in hardness between the shaft 505 and the drive hub 541. If the hardness of the hinge ball 509 (Fe--C--Cu--Ni-containing sintered material) is made lower than that of the material of the drive hub 541, the inner peripheral surface of the hinge ball 509 wears. Inversely, if the hardness of the hinge ball 509 is made higher than that of the material of the drive hub 541, the inner peripheral surface of the boss 543 of the drive hub 541 wears. In both cases, offensive noise is produced due to wear of members in sliding contact, and there is even a danger that the hinge ball 509 may be broken to lock the compressor.